1. Field of the Invention
The present invention relates to an air bleeding valve for a hydraulic tensioner of an internal combustion engine for applying a proper tension to an endless transmitting member such as an endless chain and an endless belt of power transmission in a valve train for the engine. More particularly, the present invention relates to an air bleeding valve which selectively removes air and suppresses removal of oil in a hydraulic circuit of the hydraulic tensioner, and to a hydraulic tensioner incorporating the same.
2. Description of the Background Art
An internal combustion engine mounted on a vehicle such as a motorcycle is provided with a hydraulic tensioner for pushing an endless transmitting member for driving a camshaft in a valve train, so as to prevent fluttering of the endless transmitting member during the operation of the engine.
When the operation of the engine is stopped to cause the entry of air into a hydraulic circuit of the hydraulic tensioner, there is a possibility that the hydraulic tensioner may not operate smoothly. In order to eliminate such a problem, a hydraulic tensioner having an air bleeding valve using a spherical valve element for removing the air in the hydraulic circuit in hydraulic tensioner has been proposed. An example of such hydraulic tensioner is disclosed in the Japanese Patent Document Japanese Patent No. 4017427.
In the hydraulic tensioner having the air bleeding valve in the hydraulic circuit, such as described in the Japanese Patent Document Japanese Patent No. 4017427, the spherical valve element is used in the air bleeding valve. Accordingly, when the volume of a valve chamber is increased to remove a large amount of air in a short period of time, the spherical valve element in the valve chamber is unstably moved in the valve chamber to incur vibrations, causing the turbulence of air to be removed. Further, the amount of air to be removed cannot be increased against expectation.
Further, oil from the hydraulic circuit is also removed during the removal of air, so that the load on a hydraulic pump is not reduced, resulting in poor fuel economy.
The present invention is an improvement over the existing air bleeding valve for the hydraulic tensioner that overcomes the above problems. Accordingly, it is one of the objects of the present invention to provide an air bleeding valve which can selectively remove air in a hydraulic circuit while suppressing the removal of oil in the hydraulic circuit in the initial stage of a starting operation of an internal combustion engine, and which can remove the air efficiently in a short period of time.